I know that psychology has a bad name with many out there; and for good reason. A good bit of kooky silliness (especially in the modern day) has been put out by them. Perhaps they need to justify their miserable existence, or maybe they want to install some type of false consciousness in you; but whatever the reason, what these modern types come up with is most unimpressive.
However, some old-time psychology does have some use. It is behaviorism. It is a model of how people work. It is not a perfect model. However, it does rather well for being such a simple one. The gist is this: if you provide a reward for someone is close time association with a behavior, they are more likely to repeat that behavior in the future. Also, if you punish someone for a behavior, you are less likely to get that behavior in the future.
Does this sound like how you train a dog? Why yes, yes it is. Does it apply to humans? Why yes, yes it does. Does it perhaps apply a bit more to children than adults? Yes it does, but perhaps not a much as you might think.
So, what to do? Watch people and notice how they respond to rewards and punishments, by their family, friends, employers, governments, etc. Notice what gratifications they seek, and which non-gratifying things they avoid. With a bit of thinking, it becomes clear what it happening. Often the reality with respect to adults is obscured by lots of mumbo-jumbo in an attempt to hide the true situation, especially if they are somewhat embarrassed by things. But with practice, one can see right through silliness.
So what can you do with this skill? That is rather easy: you can readily understand many seemingly complex behaviors. Furthermore, you can predict behaviors in the future. Understanding people well goes a long way to being able to navigate effectively in the world.
Exit question — What real world examples might you come up with?